Industrial and materials indexes also ended down, though above their session lows, after the Trump administration said early on Friday it was placing a 25 percent tariff on $50 billion of goods from China related to intellectual property and technology, and pledged to impose further levies if China retaliates.

Within minutes, China said it planned to retaliate and announced 25 percent tariffs on U.S. goods worth $50 billion.

The Trump administration had previously announced tariffs on imported steel and aluminum coming from several countries.

Canada and Mexico have said they will retaliate for the Washington-imposed metals tariffs.

Steel Dynamics (STLD.O) shares closed off 4.6 percent and Nucor Corp (NUE.N) shares fell 2.4 percent after both also issued financial expectations for the current quarter.

“The (steel company) earnings have been strong as a result of the tariffs the administration put in place already. Investors are worried that with the trade war escalating today it’s better to sell ... and take profits,” said Michael O’Rourke, chief market strategist at JonesTrading in Greenwich, Connecticut.

If U.S. industrial sales to China are curtailed, investors worry this would indirectly hurt demand for steel and other materials used in products, such as agricultural machinery, O’Rourke said.